14- The root must be ivarm in order to perform its fu7ictions . — 

 Should the soil of fields or greenhouses be much colder than the 

 air, we would find a very bad state of affairs for the plant. When 

 in a warm atmosphere, or in a dry atmosphere, plants need to 

 absorb much water from the soil, and the roots must be warm in 

 order that the root-hairs may be so active as to supply the water as 

 rapidly as it is needed. If the roots are chilled, then the plant 

 will wait. We may try this experimentally with two potted 

 plants, as radish, coleus, tomato, etc. Put one pot in a dish of ice 

 water, and the other in a dish of warm water, and keep them in 

 a warm room. In a short time notice how stiff and vigorous is 

 the one whose roots are warm. Perhaps the one whose roots are 

 chilled is already beginning to show signs of wilting. 



15. Roots excrete S2ibstances ivhich aid in dissolving plant-food 

 from some soil conipou7ids which are insoluble in water. — Ordinarily 

 there would be in solution in soil water only those substances 

 which are soluble in the water alone. The plant is not only pro- 

 vided for absorbing wdiat is already there in a soluble form, but it 

 is also capable of rendering soluble small quantities of the insol- 

 uble substances present in the soil, and which may be needed for 

 plant-food. The plant accomplishes this purpose by means of 

 certain excretions from the roots. In other words, not only does 

 the plant absorb dilute 

 solutions, but it gives 

 off through its root- 

 hairs small quantities 

 of acids. 



These acids may 

 even etch marble. 

 Fig. 6, from Bailey's 

 ' ' Principles of Agri- 

 culture" illustrates 

 this. " On a polished 

 marble Vjlock, place a 

 half inch of sawdust, 

 in which plant seeds. 

 After the plants have 

 attained a few leaves, turn the mass of sawdust over and observe 

 the prints of the roots on the marble." These prints will be 

 very faint. 



6. 



Root-prints in marble. The upper part repre- 

 sents the sawdust soil, turned back. 



